In a typical flywheel energy storage application a flywheel is “charged” by connecting it to a motor-generator and electrical power is input to the motor-generator to spin up the flywheel, thereby converting electrical energy to kinetic energy. The kinetic energy stored in the form of the rotational kinetic energy of the flywheel can later be extracted by connecting an electrical load to the motor-generator. To minimize losses caused by air/wind resistance, the flywheel rotor typically operates in a partial vacuum environment.
Flywheel energy storage systems have been used in a number of different applications, including in uninterruptible power supply systems and energy storage systems for frequency regulation of the utility grid. Because of their continuous operation, heat build-up in the flywheel rotor is a problem that risks early failure of the flywheel apparatus. Furthermore, cooling via convective heat transfer is limited by the partial vacuum environment in which the flywheel rotor operates.